Technical Abstract:
Twenty-five Simple Sequence Repeat (SSR) markers were used to detect molecular polymorphisms among 370 Citrus accessions from the Citrus Variety Collection located at the University of California, Riverside. The number of alleles detected per locus ranged from three to thirty. A total of 298 alleles were detected with an average of 11.88 alleles per locus and an average polymorphic information content (PIC) value of 0.633. The proportion of shared alleles was utilized as a statistical measure for determining genetic distance between all pairwise combinations. Phylogenetic relationships between the Citrus accessions and related taxa were determined by constructing a neighbor-joining tree by utilizing the genetic distance data. Additionally, individual Citrus accessions were probabilistically assigned to populations or multiple populations if their genotype indicated admixture by using a model-based clustering approach. These separate analyses (distance and model based) both support the hypothesis that there are only a few naturally occurring forms of Citrus and the rest of the Citrus species are hybrids of these naturally occurring forms.